The invention relates to a rotary piston displacement device (such as a compressor) with an impeller housing, in which an approximately cylindrical receiving chamber is provided for an approximately cylindrical rotary piston which has a smaller diameter than and is mounted eccentrically relative to, the receiving chamber, mounted on an eccentric drive, so as to form, between its outer wall and the inner wall of the receiving chamber, an approximately sickle-shaped interspace, which is divided by a separating crosspiece arranged between an inlet opening and an outlet opening located in the housing into a pressure chamber and a suction chamber. The outer and inner fixing locations of the separating crosspiece are arranged mutually offset in the peripheral direction of the rotary piston, and the separating crosspiece is formed of a flexible material.
From DE 26 28 365 A1, a rotary piston displacement device of the kind mentioned at the beginning is already known, in the impeller housing of which an approximately cylindrical receiving chamber is provided for an approximately cylindrical rotary piston, that is smaller in diameter than and mounted eccentrically relative to the receiving chamber, on an eccentric drive. This rotary piston forms between its outer wall on the one hand, and the inner wall of the receiving chamber on the other hand, an approximately sickle-shaped interspace which is divided by a separating crosspiece into a pressure chamber and a suction chamber. This separating crosspiece, the fixing locations of which are arranged mutually offset in the peripheral direction of the rotary piston, is connected on the one hand to the housing and on the other hand to the rotary piston, and can be produced from flexible material. In this connection it is explicitly mentioned in DE 26 28 365 A1 that the separating crosspiece can be produced from a flexible material, for example, a thin metal strip or a spring strip packet, or from an elastomeric material, for example, reinforced rubber, or of a composite construction from such materials, in each case the separating crosspiece always having a uniform thickness.
Although it is emphasized in DE 26 28 365 A1 that the separating crosspiece is mounted at its bead-shaped fixing locations, in a rotatable manner like a hinge in associated recesses of the rotary piston on the one hand and of the housing on the other hand, DE 26 28 365 A1 does not exclude that the separating crosspiece, also produced from, among other things, elastic or flexible materials or material layers, approximately retains the elasticity of the material from which it is made. For such a flexible separating crosspiece, however, the problem exists that the material used may still receive the tension forces arising during the operation of the previously known rotary piston displacement device, but that likewise the compressions of the separating crosspiece caused by the oscillating motion of the rotary piston can lead to undesired deformations of the separating crosspiece in the course of its longitudinal extent and thereby lead to increased material fatigue.
A so-called rotary piston compressor is also already known, which has a compressor housing with an approximately cylindrical receiving chamber. In the receiving chamber, a likewise approximately cylindrical roller piston of smaller diameter is received, mounted eccentrically to the receiving chamber on an eccentric drive. The previously known roller piston compressor has a metallic connecting member which is held in an articulated manner on the roller piston on the one hand, and on the peripheral wall bounding the receiving chamber on the other hand. The connecting member, which separates the suction chamber from the pressure chamber, consists of a circular arcuate portion provided with pin-shaped articulating members and tightly inserted into a recess in the housing wall when the roller piston passes on, whereby a gently overrunning rolling motion of the roller piston is attained. While the outlet slot is permanently connected to the pressure side, the connecting member controls with its pivoting motion the inlet slot of this otherwise valveless unit compressor.
In this previously known roller piston compressor, dynamic bearings and seals are required and constantly need sufficient lubrication. Furthermore the articulating members of the connecting member acting as hinges also need such lubrication. However, such lubrication can lead to undesired introduction of the lubricant into the material being pumped.
A displacement device has already been constructed in which a separating crosspiece held in the displacement device housing projects into a recess in the roller piston, tapering in a wedge shape in the direction toward the separating crosspiece, (cf. U.S. Pat. No. 4,157,882). This separating crosspiece is acted on by sealing strips on both sides, displaceably guided in the roller piston and sealingly pressed onto the separating crosspiece by means of compression springs.
Since only a linear sealing can be attained in the working chamber by means of the sealing strips, the working pressure which can be reached with these previously known displacement devices is rather limited. Furthermore, different metallic parts rub against each other in the region of the separating crosspiece in this previously known displacement device, so that pumping of abrasive media is prohibited and this displacement device has only a limited range of use.
A rotary piston displacement device is known from DE-OS 27 51 384, in which the sickle-shaped interspace remaining between the rotary piston outer wall and the inner wall of the receiving chamber is divided by a separating crosspiece which id formed of an elastic material. This separating crosspiece, which is oriented approximately radially to the rotary piston, is cyclically compressed and stretched at the inner wall of the receiving chamber with the rolling motion of the rotary piston on the inner wall of the receiving chamber. Because of these stretching and compression loads, the elastic material of the separating crosspiece is stressed so that the separating crosspiece connected to the rotary piston has only a comparatively short life time.
The object therefore exists of providing a durable, resilient rotary piston displacement device of the kind mentioned at the beginning, having varied usability and which is as maintenance-free as possible.
This object is attained according to the invention in that, for a rotary piston displacement device of the kind mentioned at the beginning, the separating crosspiece has bending sections near its two fixing ends, and therebetween an intermediate relatively inflexible intermediate section. The separating crosspiece, likewise produced from flexible material, of the rotary piston displacement device according to the invention has an intermediate section which is designed to be stiff to bending in comparison with the bending sections provided near the fixing locations and hence is comparatively insensitive to compressions of the separating crosspiece. The design of the separating crosspiece according to the invention permits this separating crosspiece to take up relatively large tensile forces and in particular the compressive forces which can arise due to the inertial forces acting on the separating crosspiece with a rapidly running rotary compressor. Since namely the separating crosspiece with its web end acting as articulating location on the rotary piston is moved up and down in the receiving chamber in an approximately circular arc, considerable forces act on the separating crosspiece, and the pressure or compression forces in particular can considerably stress the flexible material. In the rotary piston displacement device according to the invention, the design of the separating crosspiece intermediate section with a high bending stiffness effectively counters the deformation of the separating crosspiece in this region. In contrast to this, the flexible sections are made considerably more flexible and facilitate a hinge-like tilting of the separating crosspiece in the regions near the fixing ends.
Also, the rotary piston displacement device according to the invention has no metallic parts which rub together and which should not be exposed to abrasive media or which make necessary an additional lubrication in the region of the receiving chamber. Since the separating crosspiece, connected on the one hand to the housing and on the other hand to the rotary piston, runs approximately spirally between its outer and inner fixing locations, this separating crosspiece is exposed, when the rotary piston rolls away, only to a bending stress, but not to additional stretching and compressive loads. Since the separating crosspiece, which is formed only of flexible material, but does not necessarily have to be produced from elastic material, is acted on by comparatively small loads during the operation of the rotary piston displacement device according to the invention, the rotary piston displacement device according to the invention is distinguished in this respect by a long lifetime and varied usability. The long lifetime is further increased in that the flexible separating crosspiece is not acted on by any elastic deformation, so that work of kneading the separating crosspiece, connected with additional expenditure of energy and with increased heating, can be avoided.
A particular advantage of the rotary piston displacement device according to the invention is that the separating crosspiece follows the piston movement solely by hinge-like tilting, without any motion causing elastic deformation or friction.
It is expedient if the outer fixing location of the separating crosspiece on the housing between the inlet opening and the outlet opening, and the inner fixing location in the peripheral direction are arranged offset with respect to an outer fixing location on the rotary piston such that the separating crosspiece in the abutment position on the inner wall of the receiving chamber covers the inlet opening or the outlet opening. Thus the separating crosspiece is sealingly pressed against the inlet opening or the outlet opening during the rolling motions of the rotary piston, so that a performance-reducing backflow of the medium being forwarded can be avoided.
It can be expedient if the separating crosspiece in the abutment position on the inner wall of the receiving chamber covers the opening of the inlet channel.
A preferred embodiment, which is distinguished by an especially high performance, provides that the outer fixing location of the separating crosspiece is arranged on the housing between the inlet opening and the outlet opening, near the outlet opening, and that the inner fixing location of the separating crosspiece on the rotary piston is arranged near the inlet opening and remote from the outlet opening.
A hinge-like tilting of the separating crosspiece during the rolling motions of the rotary piston is facilitated if the separating crosspiece has bead-like shapes, preferably round or rounded in cross section, at its fixing ends, and if matching fixing recesses are provided in the housing and the rotary piston.
In order also to reduce the bending loads acting on the separating crosspiece as far as possible, and in order to still further increase the lifetime, it is expedient if the bead-like fixing shapes of the separating crosspiece project on opposite sides of its middle longitudinal plane and if the separating crosspiece is preferably formed approximately S-shaped in longitudinal section, in the widest sense.
Since the separating crosspiece of the rotary piston displacement device according to the invention does not necessarily have to be produced from elastic material. but can be formed of material which is only flexible, the separating crosspiece can, for example, be formed of flexible plastic and/or an elastomer and/or of spring steel.
In order to facilitate the bending motions of the separating crosspiece, it can be expedient if the two bending sections of the separating crosspiece have a smaller cross section than the intermediate section.
In a reversible embodiment, i.e. variable in direction of rotation, of the rotary piston displacement device according to the invention, the separating crosspiece must be able to take up the torque of the rotary piston not only as a tension force but also as a compressive force. This can be attained by a corresponding, for example thickened, shaping of the separating crosspiece and/or possibly a reinforcement worked into the separating crosspiece. Thus a preferred embodiment according to the invention provides that the intermediate section of the separating crosspiece has a reinforcement, preferably an armor inlay, to increase the compressive stiffness in the connecting plane between the fixing ends.
In order to avoid additional crushing loads acting on the separating crosspiece, it can be expedient if the housing and/or the rotary piston have recesses in the peripheral course of the separating crosspiece for at least partially receiving the separating crosspiece.
A short circuit between the pressure chamber and the suction chamber can be effectively avoided if at least one peripherally closed seal is provided laterally near the rotary piston between at least one of its sidewalls and the housing or respectively a drive shaft guide. Here ring seals and/or bellows seals can be provided as the seals.
An advantageous embodiment according to the invention provides that the rotary piston displacement device is provided as a compressor, and that the compressor preferably has at least one outlet valve.
Another advantageous embodiment according to the invention is provided in that the rotary compressor is part of a compressed air motor and that for this at least two rotary compressors are provided, arranged axially adjacent with rotary pistons offset in the direction of rotation, preferably by 180xc2x0. If the rotary pistons are arranged offset by 180xc2x0, an overflow of compressed air between the inlet and outlet opening is prevented at the 12-o""clock position. In this manner, starting of the motor from any position is ensured.
Developments according to the invention are shown in further claims.